The Assignee has developed mobile phones, personal data assistants (PDAs) and other mobile telecommunication devices, with the ability to print hard copies of images or information stored or accessed by the device (see for example, U.S. Pat. No. 6,405,055, filed on Nov. 9, 1999). Likewise, the Assignee has also designed digital cameras with the ability to print captured images with an inbuilt printer (see for example, U.S. Pat. No. 6,750,901 filed on Jul. 10, 1998). As the prevalence of mobile telecommunications devices with digital cameras increases, the functionality of these devices is further enhanced by the ability to print hard copies.
As these devices are portable, they must be compact for user convenience. Accordingly, any printer incorporated into the device needs to maintain a small form factor. Also, the additional load on the battery should be as little as possible. Furthermore, the consumables (ink and paper etc) should be relatively inexpensive and simple to replenish. It is these factors that strongly influence the commercial success or otherwise of products of this type. With these basic design imperatives in mind, there are on-going efforts to improve and refine the functionality of these devices.
The Assignee of the present invention has also developed the Netpage system for enabling interaction with computer software using a printed interface and a proprietary stylus-shaped sensing device.
As described in detail in U.S. Pat. No. 6,792,165, filed on Nov. 25, 2000 and U.S. patent application U.S. Ser. No. 10/778,056, filed on Feb. 17, 2004 a Netpage pen captures, identifies and decodes tags of coded data printed onto a surface such as a page. In a preferred Netpage implementation, each tag encodes a position and an identity of the document. By decoding at least one of the tags and transmitting the position (or a refined version of the position, representing a higher resolution position of the pen) and identity referred to by the decoded tag, a remote computer can determine an action to perform. Such actions can include, for example, causing information to be saved remotely for subsequent retrieval, downloading of a webpage for printing or display via a computer, bill payment or even the performance of handwriting recognition based on a series of locations of the Netpage pen relative to the surface. These and other applications are described in many of the Netpage-related applications cross-referenced by the present application.
When printing onto a print medium, it is desirable to in some cases to determine movement of the print medium during printing to enable the printing to be synchronized. Usually this is done by determining the speed of drive rollers and inferring print medium speed. However, where drive rollers are very small, this can be an unreliable method of determining movement. It would be desirable to provide a way of determining movement of a print medium during printing that does not rely on measuring roller movement.